CONTENTS OF CELLS. 9 



When small portions of vegetable tissue are soated in Beale's Car- 

 mine solution, only those ceUs containing protoplasm appear stained. 

 The nuclei and granules in the protoplasm seem alone to he affected. 

 The depth of colouring depends on the number of granules in the 

 protoplasm and the size of the nuclei. 



In certain cells the membranous wall consists throughout life 

 of a thin layer .of cellulose, while in others it becomes thickened by 

 the deposition of matter on its inner side. These secondary deposits 

 are sometimes of a gelatmous consistence; at other times they are 

 hard. In the latter case, the matter is looked upon as a modification 

 of cellulose, and has received the name of lignin (lignum, wood), or 

 scUrogm (sxXri^hg, hard, and ymaeiv, to generate). On making sec- 

 tions of such cells, in a transverse (fig. 31) or longitudmal direction 

 (fig. 32), the successive layers may be seen 

 either continuous all round, or leaving parts 

 of the membrane uncovered. Cells of this 

 kind are well seen under the microscope in 

 thin sections of the hard shell of the Coco-nut, 

 and Attalea funifera, and of the hard seed 

 of the- Ivory Palm. In all cell deposits there 

 is a tendency to a spiral arrangement. When ^- • 



the deposition is uniform over the whole surface, this arrangement 

 may not' be detected; but when interruptions take place, thep the 

 continued coil becomes evident. In spiral cells the fibre seems to be 

 formed before the fuU development of the cell, the coils of the fibre 

 being at first in contact, and afterwards separated, whereas the second- 

 ary thickening layers are deposited after the cell is fully formed. Ac- 

 cording to the observations of Barry, Agardh, and others, the filamentous 

 origin of fibrous structures is recognisable in the earliest stage of cell 

 growth, and the interweaving of these filaments constitutes the cell- walls. 



Each cell is found to contain at some period of its existence a 

 small body called a nucleus (fig. 33, n n n), in which 

 there are often one or two, rarely more, minute spots /~\__i*'\ » 

 called nucleoli. The nucleus is of a round or oval ( '^ /LA/^ 

 shape, granular and dark, or homogeneous and trans- )~\__i~Lv " 

 parent, bearing some resemblance to a smaller in- f® ji /~j 

 ternalcell. -Nucleoli are not always present. They are ^~{_/~w " 

 either vesicles and granules contained in the nucleus, '~' 

 or minute cavities in its substance. The latter view * 



is supported by Barry, who holds that a peculiar substance called hyaline 

 (uaXog, glass) is developed there, which, according to him, is the origin 

 of the nucleus. The nucleus is situated at difierent parts of the cell. 

 It is either free in its cavity, or connected with its walls by mucilaginous 



Fig. 31. Transverse section of cells from pulp of Pear. Fig. 32. Longitudinal section 

 of the same. Fig. 33. Nucleated cells from the Beet. 



